Polyols for use in preparing polyurethanes are usually prepared by the reaction of an initiator compound having active hydrogens with an alkylene oxide in the presence of a basic catalyst such as a tertiary amine, sodium and potassium hydroxide or alkoxide. However, the use of these catalysts, although commonplace, leads to the production of polyols which can contain high levels of unsaturation, especially when such polyols are of high equivalent weight.
In the base-catalyzed addition of propylene oxide to initiators containing active hydrogens, the growing polyether chains are terminated predominantly with secondary hydroxy groups. However, under the conditions of the reaction, temperature, pressure and catalyst concentration, the propylene oxide may isomerize to give an allyl alcohol before it can react with the initiator.
The ability to prepare high equivalent weight products in the presence of the allyl alcohol is reduced as these compounds themselves contain an active hydrogen which can react with propylene oxide. The problem of unsaturation becomes more severe as the equivalent weight of the polyol becomes greater.
The types of terminal unsaturation and means of reducing it by acid treatment of the end product are discussed by Dege et al., Journal of the American Chemical Society, p. 3374, Vol. 81 (1959).
When polyols of high equivalent weight and high unsaturation are used in the preparation of polyurethane polymers such as flexible foams, products with undesirable properties can result. Problems such as foam discoloration, inferior compressive and tensile strengths, low reactivity, low flexural modulus and poor humid aging may be encountered.
Unsaturation in polyols to be used in preparing polyurethane polymers can be reduced by acid treatment of the product resulting from the reaction of an initiator with alkylene oxide as described in U.S. Pat. Nos. 2,996,550 and 3,271,462.
U.S. Pat. No. 3,393,243 teaches the use of the Group IA metal catalyst caesium hydroxide for the preparation of polyoxypropylene polyether polyols having an equivalent weight of 1500 to 2500 and reduced levels of unsaturation. This catalyst is much more costly than the alternative basic catalysts, as it is required in larger quantities to operate at an equivalent molar concentration due to the high molecular weight of caesium.
The use of caesium hydroxide as catalyst in the alkoxylation reaction of alcohols giving products with low unsaturation levels has recently been documented, see patents EP 268,922-A and EP 268,920-A.
It is desirable to develop a process which can achieve the preparation of polyether polyols with reduced unsaturation and reduce or eliminate the use of expensive catalysts such as caesium hydroxide and/or the acid treatment of the reaction product.
The use of barium-containing catalysts in the presence of catalyst promoters is described for the ethoxylation reactions of alkanols to make nonionic surfactants, see, for example, U.S. Pat. No. 4,210,764; 4,239,917 and EP 46,647.
The Japanese patent 55/092,733-A teaches the use of barium hydroxide in combination with a carbon dioxide finishing process for the preparation of preferably ethylene oxide containing polyether polyols having equivalent weights of 187 or less. The products so produced are suitable for the preparation of rigid or semi-rigid polyurethane foam due to their very low residual alkoxylation catalyst content.